某海上油田海水管线系统发生泄漏, 经调查确认为某铜镍合金弯头腐蚀穿孔所致。针对弯头腐蚀失效分析开展了宏观分析、理化性能检验、扫描电镜及能谱分析, X射线衍射(XRD)分析等。结果表明: 弯头铸造加工缺陷引发的流动诱导腐蚀是导致弯头腐蚀穿孔的主要原因; 焊缝钝化效果不良, 是导致弯头腐蚀穿孔次要原因。建议以后对新购进铜镍合金铸造构件加强质检, 确保质量合格; 确保焊接质量前提下, 焊缝充分钝化, 确保形成保护性氧化膜。

A leakage occurred in certain offshore oilfield seawater pipeline system. It was confirmed by investigation that the leakage was because of the corrosion perforation of a pipeline elbow made of Cu-Ni alloy. The failure causes of the corrosion perforation in the elbow were studied by macro analysis, physical and chemical properties testing, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results show that turbulent flow resulted from the defects produced in casting process caused flow-induced corrosion, which was the prime reason for corrosion perforation of the elbow wall. The area near the weld seam with poor passivation quality became the weak spot in the whole system and was prone to corrosion damage. Consequently, it is important to perform quality inspection to newly purchased elbow to ensure quality, and the weld seam should be thoroughly passivated to ensure the formation of protective oxide film.